The present invention is directed toward switches and more particularly toward test switches.
Relays are commonly used in electric utility applications to detect various possible problems in the electrical power output and, thus, protect very expensive equipment such as motors and generators. These protective relays are used in relay systems which also include circuit breakers. Relays and circuit breakers must function together because the primary function of the relays is to trip the circuit breakers.
Protective relays constantly monitor the power systems to assure maximum continuity of electrical service with minimum damage to life and property. Protective relays are used in applications extending from the generation and transmission of power, through the distribution and utilization of the power. Examples of such applications include, without limitation, motor, generator, transformer, station-bus, line and circuit, system ground, network systems, pilot wire, pilot channel, transmission line, pilot relying, backup, reclosing, synchronizing and load-shedding. In general, current transformers and potential transformers are employed in high current and high potential applications.
The transformers reduce the magnitude of the current or voltage, which is then fed to the relays, meters and instruments at a much lower level for detection. The relay terminals are then connected to a test switch terminal or poles. Each test switch can be associated with one or more relays. It is necessary to short circuit the line and load terminals when the relay is removed from its case or the adjacent test switch is opened. The test switch provides this necessary short circuit or bypass feature. If this short circuit does not occur there could be significant damage to the associated current transformer as well as a safety hazard to nearby personnel.
One example of a prior art test switch is the Flexitest™ test switch 10 shown in FIG. 1a which is sold by ABB Inc. of Coral Springs, Fla. The variety and extensive types of test switches available allows for many types of applications. As is well known to those of ordinary skill in the art these applications include but are not limited to a test switch with all potential switches, that is, no switches associated with current transformers, or all of the switches in a test switch associated with current transformers.
Test switch 10 includes on its front face 10 switches 12a to 12j arranged in five (5) sets. In the embodiment shown in FIG. 1a, the test switch 10 has three (3) sets of switches, namely 12a and 12b, 12c and 12d, and 12e and 12f which are associated with a respective one of three (3) current transformers (not shown). As is well known, each current transformer is associated with a respective one of the three (3) phases of a three phase power source. Test switch 10 also includes four potential switches 12g, 12h, 12i and 12j, with one of the four switches associated with phase A of the three phase source, a second of the four switches associated with phase B of the three phase source, a third of the four switches associated with phase C of the three phase source and the fourth switch associated with the neutral of the three phase power source.
One example of the three sets of switches associated with a current transformer are shown in FIG. 1b. The two switches in each of the three sets of switches associated with a current transformer include a switch such as switch 12a, 12c or 12e which has a shorting blade 14 and a switch such as switch 12b, 12d or 12f which does not have a shorting blade. The switch 12a, 12c or 12e with the shorting blade provides when opened the desired short circuit of the line and load terminals when that switch is opened. The switch 12b, 12d or 12f without the shorting blade provides a current test jack 16.
Test switch 10 also includes on it rear face twenty terminals only ten of which 18a to 18j are shown in FIG. 1a for connection to the relays associated with the current transformers and the three phases and neutral of the three phase source. When test switch 10 is mounted in a switchboard panel (not shown) the switches 12a to 12j are accessible from the front of the panel, while the terminals 18a to 18j and the other ten rear face terminals not shown in FIG. 1a are accessible only from the rear of the panel.
Although prior art test switches, such as the test switch 10, have proven to be an effective means of implementing connections to all types of relays, meters and instruments, such switches are not without their drawbacks. Typically, the terminals (such as 18a to 18j) are only accessible from the rear of the test switch. Moreover, only one type of terminal connection is provided, namely either a stud connection, or a nut connection.
Based on the foregoing, there exists a need in the art for a test switch having terminals that are accessible from the front of the test switch and have different types of terminal connections. The present invention is directed to such a test switch.